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PubMed2005

Examining the influence of drop-outs in a follow-up of maintained opiate users.

INTRODUCTION: In most longitudinal studies of problem opiate users, drop-outs are frequent, but not taken into account. However, missing data can induce important bias in parameters estimates. OBJECTIVE: The aim of this study was to examine the influence of drop-outs in the statistical analysis of a follow-up of opiate users in maintenance treatment. METHODS: Participants were 519 patients who had sought maintenance treatment between 1994 and 2001. Drug use was studied using the drug composite score of the Addiction Severity Index. A classical data analysis (linear mixed effects model for repeated measurements) was compared with a selection model, which consists, in this case, of a joint modelling of the score and of the drop-out probability in order to reduce bias induced by drop-outs. RESULTS: At 18 months, 38% of the patients were available for evaluation. Drop-outs were associated with low drug use and were informative. Each model showed that the score decreased over time and that it was associated with psychiatric problems. Unlike the classical method, the joint model showed no significant association between the score and age or treatment setting. CONCLUSIONS: These results show the importance of accounting for informative drop-outs in data analysis before drawing conclusions from such studies.

Adult↗
PubMed1998

Group cognitive-behavioral treatment of binge eating disorder: a comparison of therapist-led versus self-help formats.

OBJECTIVE: The purpose of this study was to compare three group cognitive-behavioral therapy (CBT) treatment models and a waiting list control condition (WL). METHOD: Sixty-one women who met DSM-IV criteria for binge eating disorder (BED) received treatment with the same cognitive-behavioral treatment manual in 14 one-hour sessions over an 8-week period. All sessions consisted of psychoeducation for the first 30 min and group discussion for the second half hour. In the therapist-led condition (TL; n = 16), a doctoral therapist led both the psychoeducational component and group discussion. In the partial self-help condition (PSH; n = 19), participants viewed a 30-min psychoeducational videotape, followed by participation in a therapist-led discussion. In the structured self-help condition (SH; n = 15), subjects viewed the 30-min psychoeducational videotape and subsequently led their own 30-min discussion. Eleven subjects were assigned to a wait-list control condition (WL). The primary outcome variables were frequency and duration of self-reported binge eating episodes. RESULTS: A mixed effects linear modeling (random regression) analysis indicated that subjects in all three active treatment conditions showed a decrease in binge eating symptoms over time. No group differences in rates of change over time were observed, although analysis of covariance indicated that all three treatment conditions showed significantly greater improvement in binge eating compared to the WL condition. DISCUSSION: The findings from this preliminary study suggest that CBT for BED can be delivered effectively in a structured group self-help format.

Adolescent↗
PubMed2006

Inference for magnitudes and delays of responses in the FIAC data using BRAINSTAT/FMRISTAT.

We used straightforward linear mixed effects models as described in Worsley et al. together with recent advances in smoothing to control the degrees of freedom, and random field theory based on discrete local maxima. This has been implemented in BRAINSTAT, a Python version of FMRISTAT. Our main novelty is voxel-wise inference for both magnitude and delay (latency) of the hemodynamic response. Our analysis appears to be more sensitive than that of Dehaene-Lambertz et al. Our main findings are greater magnitude (1.08% +/- 0.17%) and delay (0.153 +/- 0.035 s) for different sentences compared to same sentences, together with a smaller but still significantly greater magnitude for different speaker compared to same speaker (0.47% +/- 0.08%).

Algorithms↗
PubMed2006

Preconceptional fasting of fathers alters serum glucose in offspring of mice.

OBJECTIVE: Maternal nutrition has long-term effects on offspring characteristics. Similar effects mediated through fathers have not been tested. METHODS: Outbred Swiss male mice were fasted one or six times 1 to 4 wk before mating. Offspring were killed at age intervals of 4 to 10 wk and their sera were analyzed for glucose, corticosterone, and insulin-like growth factor-1. Statistical linear mixed effects models were used to determine treatment (paternal diet restriction versus control) differences and possible effects of covariates, including sex, litter membership, and litter size. RESULTS: Paternal food deprivation resulted in a consistent decrease in average serum glucose in male and female offspring. Significant changes in corticosterone and insulin-like growth factor-1 were found for some groups. The results indicated a male-mediated transgenerational effect on metabolism- and growth-related parameters, in particular glucose. CONCLUSIONS: Effects of paternal nutritional experiences on offspring metabolism, if confirmed, would be novel and could have far-reaching implications in the context of transgenerational effects on chronic diseases.

Animals↗
PubMed2004

Peripartum serum vitamin E, retinol, and beta-carotene in dairy cattle and their associations with disease.

Peripartum decreases in serum concentrations of vitamins A and E may contribute to impaired immune function in dairy cows. The objectives of this study were to describe peripartum serum concentrations of alpha-tocopherol, beta-carotene, and retinol and their associations with disease risk. On 20 farms over 1 yr, blood samples were collected weekly from 1057 cows from 1 wk before expected calving until 1 wk postpartum. Serum concentrations of alpha-tocopherol, beta-carotene, and retinol, as well as several biochemical variables were measured. Their associations with the risk of retained placenta or clinical mastitis were modeled separately with logistic regression, and the factors associated with the concentration of each vitamin were modelled with mixed linear regression. Differences in vitamin concentrations between 2 batches of sera analyzed 6 mo apart required stratification of statistical analyses. Accounting for the effects of parity, season, and twins, an increase in alpha-tocopherol of 1 microg/mL in the last week prepartum reduced the risk of retained placenta by 20%, whereas serum nonesterified fatty acid concentration > or = 0.5 mEq/L tended to increase risk of retained placenta by 80%. In the last week prepartum, a 100 ng/mL increase in serum retinol was associated with a 60% decrease in the risk of early lactation clinical mastitis. There were significant positive associations of peripartum serum concentrations among each of alpha-tocopherol, beta-carotene, and retinol.

Animals↗
PubMedDate not supplied

Gender differences in quality of life among cardiac patients.

OBJECTIVE: Prior studies of quality of life among cardiac patients have examined mostly men. This study evaluated gender differences in quality of life and examined the degree to which social support was associated with quality of life. METHODS: A sample of 536 patients (35% women) was recruited during a 14-month period from the inpatient cardiology service of a University-based hospital. Participants completed assessments at baseline and at 3-month intervals over the subsequent 12 months, for a total of 5 assessments. Measures at each assessment included quality of life [Mental Component Score (MCS) and Physical Component Score (PCS) from the Medical Outcomes Study--Short Form 36] and social support [Interpersonal Support Evaluation List--Short Form]. RESULTS: A total of 410 patients completed the baseline assessment and at least one follow-up, and were included in the data analyses. Linear mixed effects modeling of the MCS score revealed a significant effect of gender (p =.028) and time (p <.001), as well as a significant interaction of gender by social support (p =.009). Modeling of the PCS revealed a significant effect of gender (p =.010) and time (p <.001). CONCLUSIONS: Women with cardiac disease indicated significantly lower quality of life than men with cardiac disease over the course of a 12-month longitudinal follow-up. Social support, especially a sense of belonging or companionship, was significantly associated with emotional quality of life (MCS) among women. Strategies to increase social support may be important for health and well-being of women with cardiac disease.

Adult↗
PubMed2003

Are facial expressions reproducible?

OBJECTIVES: To determine the extent of reproducibility of five facial expressions. DESIGN: Thirty healthy Caucasian volunteers (15 males, 15 females) aged 21 to 30 years had 20 landmarks highlighted on the face with a fine eyeliner pencil. Subjects were asked to perform a sequence of five facial expressions that were captured by a three-dimensional camera system. Each expression was repeated after 15 minutes to investigate intrasession expression reproducibility. To investigate intersession expression reproducibility, each subject returned 2 weeks after the first session. A single operator identified 3-dimensional coordinate values of each landmark. A partial ordinary procrustes analysis was used to adjust for differences in head posture between similar expressions. Statistical analysis was undertaken using analysis of variance (linear mixed effects model). RESULTS: Intrasession expression reproducibility was least between cheek puffs (1.12 mm) and greatest between rest positions (0.74 mm). The reproducibility of individual landmarks was expression specific. Except for the lip purse, the reproducibility of facial expressions was not statistically different within each of the two sessions. Rest position was most reproducible, followed by lip purse, maximal smile, natural smile, and cheek puff. Subjects did not perform expressions with the same degree of symmetry on each occasion. Female subjects demonstrated significantly better reproducibility with regard to the maximal smile than males (p =.036). CONCLUSIONS: Under standardized conditions, intrasession expression reproducibility was high. Variation in expression reproducibility between sessions was minimal. The extent of reproducibility is expression specific. Differences in expression reproducibility exist between males and females.

Adult↗
PubMed1996

Angiotensin-converting enzyme inhibition in nondiabetic progressive renal insufficiency: a controlled double-blind trial.

Angiotensin-converting enzyme inhibitors delay progression of renal disease in different animal models of nephropathy. We tested this treatment modality in 70 hypertensive patients with severe renal disease of various etiologies. We report a double-blind study of the effect of 5 mg enalapril once daily compared with placebo in patients with nondiabetic severe chronic renal impairment (plasma creatinine 2.8 to 6.8 mg/dL; mean creatinine clearance 15 mL/min/1.73 m2) followed for up to 2 years. Efficacy parameters were the slopes of 51Cr-EDTA clearance, reciprocal of plasma creatinine, creatinine clearance, and the effect on urinary protein excretion. Thirty-one patients completed 2 years of treatment (12 in the enalapril group and 19 in the placebo group). Two patients died from nonrenal causes (one patient each in the enalapril and placebo groups), 16 patients commenced dialysis (seven in the enalapril group and nine in the placebo group), and eight patients were discontinued due to adverse events (five in the enalapril group and three in the placebo group). Eleven patients were discontinued because they were noncompliant, uncooperative, or moved (nine in the enalapril group and two in the placebo group). Two enalapril-treated patients were dropped from the study due to protocol deviations. Importantly, the statistical approach in this study evaluated all patients, regardless of the duration of treatment. A mixed-effects linear model and intention to treat analysis, taking into account the number of observations per patient, indicated that enalapril significantly reduced the rate of deterioration of renal disease: glomerular filtration rate (P = 0.038), reciprocal of plasma creatinine (P = 0.017), or creatinine clearance (P = 0.031). The renal protective effects of enalapril were shown to be in addition to its antihypertensive effect when blood pressure was held constant. Proteinuria was reduced by enalapril (P = 0.007) and was slightly increased in the placebo-treated patients (P = 0.051). The difference between these two groups was highly significant (P = 0.002). In conclusion, enalapril retarded the progression of chronic renal failure, as assessed by changes in glomerular filtration rate, creatinine clearance, and 1/plasma creatinine, and reduced proteinuria in patients with nondiabetic severe chronic renal insufficiency.

Adolescent↗
PubMed2005

Pharmacokinetics of low-dose doxorubicin and metabolites in patients with AIDS-related Kaposi sarcoma.

PURPOSE: Systemic chemotherapy is the treatment of choice for AIDS-related advanced Kaposi sarcoma. One principal schedule combines adriamycin (doxorubicin), bleomycin, and vincristine (ABV). We analysed the plasma concentrations of low-dose doxorubicin (Dx) and its metabolites doxorubicinol, 7-deoxydoxorubicinone, doxorubicinone, doxorubicinolone, and 7-deoxydoxorubicinolone in AIDS-patients to define patient-group and dose-specific pharmacokinetic parameters. MATERIALS AND METHODS: A previously described high-performance liquid chromatographic (HPLC) method and a population approach with non-linear mixed effects modelling (NONMEM) were used for analysis and subsequent modelling of the time-concentration data of low-dose Dx and metabolites in seven patients with AIDS-related advanced Kaposi sarcoma. Patients received Dx 20 mg m(-2), bleomycin 15 U m(-2) and vincristine 2 mg as a 30-min intravenous infusion each. Blood samples were collected up to 72 h after the start of Dx treatment. WinNonlin software version 4.1 was used for non-compartmental analysis and NONMEM software version V for compartmental analysis. Covariate analysis was performed for various clinical and laboratory parameters. RESULTS: Non-compartmental analysis yielded an area under the plasma concentration-time curve (AUC) for Dx of 566 mug h L(-1), a maximum plasma concentration (c(max)) of 599 mug L(-1) and an elimination half-life (t(1/2)) of 30.8 h. Compartmental analysis resulted in a two-compartment model with first-order elimination, which best fitted the concentration-time data. Model estimate for Dx clearance was 61.8 L h(-1), for intercompartmental clearance (Q) 112 L h(-1), for the volume of the central compartment (V(1)) 23.3 L, and for the volume of the peripheral compartment (V(2)) 1,130 L. Metabolite data could adequately be estimated by NONMEM using single-compartment models. Graphical plots of residuals versus time for all metabolites yielded no evidence of non-linear pharmacokinetic behaviour. Laboratory parameters of liver and renal function were all in the normal range and their inclusion in the pharmacokinetic model did not improve data fit. A final jack-knife analysis was performed. CONCLUSIONS: Concentration-time data for low-dose Dx and metabolites in the ABV-regimen are best described by a two-compartment model with first-order elimination. The results confirm that the aglycones doxorubicinone, 7-deoxydoxorubicinone, and doxorubicinolone can be reliably detected in the studied patient group and implemented into a common metabolic model. Model estimates suggest that pharmacokinetic parameters are similar for low-dose Dx and higher-dosed Dx. As the role of the aglycones is still poorly understood, despite their potential clinical relevance, their analysis should be implemented in future pharmacokinetic and pharmacodynamic studies of Dx.

AIDS-Related Opportunistic Infections↗
PubMed2006

Repeated measurement of nasal lavage fluid chemokines in school-age children with asthma.

BACKGROUND: Inflammatory processes at the mucosal surface may play a role in maintenance of asthma pathophysiology. Cross-sectional studies in asthmatic patients suggest that chemokines such as interleukin 8 (IL-8) are overproduced by respiratory epithelium. OBJECTIVE: To test the hypothesis that chemokine levels are persistently elevated in the respiratory secretions of asthmatic children at a stable baseline. METHODS: We measured nasal lavage fluid (NLF) levels of chemokines and other mediators at 3- to 4-month intervals in a longitudinal study of asthmatic children, with nonasthmatic siblings as controls. RESULTS: In a linear mixed-model analysis, both family and day of visit had significant effects on nasal mediators. Thus, data for 12 asthmatic-nonasthmatic sibling pairs who had 3 or more same-day visits were analyzed separately. For sibling pairs, median eosinophil cationic protein levels derived from serial measurements in NLF were elevated in asthmatic patients compared with nonasthmatic patients, with a near-significant tendency for elevation of total protein and eotaxin levels as well. However, no significant differences were found for IL-8 or several other chemokines. Ratios of IL-13 or IL-5 to interferon-gamma released by house dust mite antigen-stimulated peripheral blood mononuclear cells, tested on a single occasion, were significantly increased for asthmatic patients. CONCLUSIONS: Substantial temporal and family-related variability exists in nasal inflammation in asthmatic children. Although higher levels of eosinophil cationic protein are usually present in NLF of patients with stable asthma compared with patients without asthma, chemokines other than eotaxin are not consistently increased. Eosinophil activation at the mucosal surface is a more consistent predictor of asthmatic symptoms than nonspecific elevation of epithelium-derived inflammatory chemokine levels.

Adolescent↗
PubMed2003

Number of days, number of subjects, and sources of variation in longitudinal intervention or crossover feeding trials with multiple days of measurement.

Dietary studies are often conducted as longitudinal intervention or crossover trials using multiple days of measurement on each subject during each of several measurement periods, and determining the required numbers of days and subjects is important in designing these studies. Linear mixed statistical models were used to derive equations for precision, statistical power and sample size (number of days and number of subjects) and to obtain estimates of between-subject, period-to-period, and day-to-day variation needed to apply the equations. Two cohorts of an on-going exercise intervention study, and a crossover study of Olestra, each with 14 d of measurement/subject per period, were used to obtain estimates of variability for energy and macronutrient intake. Numerical examples illustrate how the equations for calculating the number of days or number of subjects are applied in typical situations, and sample SAS code is given. It was found that between-subject, period-to-period, and day-to-day variation all contributed significantly to the variation in energy and macronutrient intake. The ratio of period-to-period and day-to-day standard deviations controls the trade-off between the number of days and the number of subjects, and this remained relatively stable across studies and energy and macronutrient intake variables. The greatest gains in precision were seen over the first few measurement days. Greater precision and fewer required days were noted in the study (Olestra) that exerted greater control over the subjects and diets during the feeding protocol.

Adult↗
PubMed2006

Are physicians' attitudes of respect accurately perceived by patients and associated with more positive communication behaviors?

OBJECTIVE: To explore the domain of physician-reported respect for individual patients by investigating the following questions: How variable is physician-reported respect for patients? What patient characteristics are associated with greater physician-reported respect? Do patients accurately perceive levels of physician respect? Are there specific communication behaviors associated with physician-reported respect for patients? METHODS: We audiotaped 215 patient-physician encounters with 30 different physicians in primary care. After each encounter, the physician rated the level of respect that s/he had for that patient using the following item: "Compared to other patients, I have a great deal of respect for this patient" on a five-point scale between strongly agree and strongly disagree. Patients completed a post-visit questionnaire that included a parallel respect item: "This doctor has a great deal of respect for me." Audiotapes of the patient visits were analyzed using the Roter Interaction Analysis System (RIAS) to characterize communication behaviors. Outcome variables included four physician communication behaviors: information-giving, rapport-building, global affect, and verbal dominance. A linear mixed effects modeling approach that accounts for clustering of patients within physicians was used to compare varying levels of physician-reported respect for patients with physician communication behaviors and patient perceptions of being respected. RESULTS: : Physician-reported respect varied across patients. Physicians strongly agreed that they had a great deal of respect for 73 patients (34%), agreed for 96 patients (45%) and were either neutral or disagreed for 46 patients (21%). Physicians reported higher levels of respect for older patients and for patients they knew well. The level of respect that physicians reported for individual patients was not significantly associated with that patient's gender, race, education, or health status; was not associated with the physician's gender, race, or number of years in practice; and was not associated with race concordance between patient and physician. While 45% of patients overestimated physician respect, 38% reported respect precisely as rated by the physician, and 16% underestimated physician respect (r=0.18, p=0.007). Those who were the least respected by their physician were the least likely to perceive themselves as being highly respected; only 36% of the least respected patients compared to 59% and 61% of the highly and moderately respected patients perceived themselves to be highly respected (p=0.012). Compared with the least-respected patients, physicians were more affectively positive with highly respected patients (p=0.034) and provided more information to highly and moderately respected patients (p=0.018). CONCLUSION: Physicians' ratings of respect vary across patients and are primarily associated with familiarity rather than sociodemographic characteristics. Patients are able to perceive when they are respected by their physicians, although when they are not accurate, they tend to overestimate physician respect. Physicians who are more respectful towards particular patients provide more information and express more positive affect in visits with those patients. PRACTICE IMPLICATIONS: Physician respectful attitudes may be important to target in improving communication with patients.

Adolescent↗
PubMed2001

Use of medications with anticholinergic effect predicts clinical severity of delirium symptoms in older medical inpatients.

BACKGROUND: Use of anticholinergic (ACH) medications is a biologically plausible and potentially modifiable risk factor of delirium, but research findings are conflicting regarding its association with delirium. OBJECTIVES: To evaluate the longitudinal association between use of ACH medications and severity of delirium symptoms and to determine whether this association is modified by the presence of dementia. PATIENTS AND METHODS: A total of 278 medical inpatients 65 years and older with diagnosed incident or prevalent delirium were followed up with repeated assessments using the Delirium Index for up to 3 weeks. Exposure to ACH and other medications was measured daily. The association between change in medication exposure in the 24 hours preceding a Delirium Index assessment was assessed using a mixed linear regression model. RESULTS: During follow-up (mean +/- SD, 12.3 +/- 7.0 days), 47 medications with potential ACH effect were used in the population (mean, 1.4 medications per patient per day). Increase in delirium severity was significantly associated with several measures of ACH medication exposure on the previous day, adjusting for dementia, baseline delirium severity, length of follow-up, and number of non-ACH medications taken. Dementia did not modify the association between ACH medication use and delirium severity. CONCLUSION: Exposure to ACH medications is independently and specifically associated with a subsequent increase in delirium symptom severity in elderly medical inpatients with diagnosed delirium.

Aged↗
PubMed2004

Racial differences in optic disc topography: baseline results from the confocal scanning laser ophthalmoscopy ancillary study to the ocular hypertension treatment study.

OBJECTIVE: To examine racial differences in optic disc topography among ocular hypertensive participants in the Ocular Hypertension Treatment Study. METHODS: Four hundred thirty-nine participants from 7 Ocular Hypertension Treatment Study centers who had good-quality baseline images obtained using a quantitative 3-dimensional confocal scanning laser ophthalmoscope, the Heidelberg Retina Tomograph (Heidelberg Engineering, Dossenheim, Germany), were included in this study. The first 10 degrees- or 15 degrees-field of view mean topographic image acquired was included in all analyses. Differences in Heidelberg Retina Tomograph topographic optic disc parameter measurements by self-identified race were assessed using a mixed-effects linear model to control for confounders and for the use of both eyes in the model. RESULTS: By self-attribution, 74 (17%) of the 439 participants were of African origin, 329 (75%) were white, 24 (5%) were Hispanic, and 12 (3%) were Native American, Native Alaskan, Asian, Pacific Islander, or unknown. The African American participants had statistically significantly (P<.001) larger mean (SD) optic disc areas than the other participants, 2.17 (0.41) mm(2) vs 1.87 (0.38) mm(2), respectively. African American participants had a larger cup area, cup volume, cup depth, neuroretinal rim area, rim volume, and smaller rim-optic disc area ratios than the other participants. No difference between African American and the other participants was found for cup shape and retinal nerve fiber layer thickness. After controlling for optic disc area, none of the differences between African American and the other participants found in the univariate analysis remained statistically significant (P>.10). CONCLUSIONS: This study demonstrated in a large cohort of subjects with ocular hypertension, that African Americans have significantly larger optic discs, optic cups, neuroretinal rims, and cup-disc ratios than other racial groups. Furthermore, this study found that differences in topographic optic disc parameters between African Americans with ocular hypertension and other racial groups are largely explained by the larger optic disc area in the African Americans. These results highlight the need to consider race and optic disc size when evaluating the appearance of the optic disc in glaucoma.

Antihypertensive Agents↗
PubMed1997

Testing homogeneity of intra-run variance parameters in immunoassay.

A common assumption in the analysis of immunoassay data is a similar pattern of within-run variation across runs of the assays. One makes this assumption without formal investigation of its validity, despite the widely acknowledged fact that accurate understanding of intra-run variation is critical to reliable calibration inference. We propose a simple procedure for a formal test of the assumption of the homogeneity of parameters that characterize intra-run variation based on representation of standard curve data from multiple assay runs by a non-linear mixed effects model. We examine the performance of the procedure and investigate the robustness of calibration inference to incorrect assumptions about the pattern of intra-run variation.

Calibration↗
PubMed2000

Citric acid etching of cervical sclerotic dentin lesions: an AFM study.

Atomic force microscopy (AFM) has been used to determine microstructural changes, etching rates of peritubular dentin, and intertubular dentin recession during demineralization in dilute acidic solutions. These studies have not included many forms of altered dentin, including noncarious sclerotic root dentin associated with Cl V (abfraction) lesions. We sought to determine microstructural changes and recession rates during demineralization in citric acid (pH 2.5, 0.018M) for the transparent/sclerotic zone. Highly polished dentin disks were prepared from teeth with noncarious C1 V lesions (n = 3) and compared with normal root dentin (n = 3). Samples were etched at 5-s intervals for 1 min and at longer intervals up to 30 min. The depth changes in various portions of the dentin with respect to the reference layer were measured and changes in microstructure observed in solution in the wet cell of the AFM. In sclerotic dentin, most tubule lumens were occluded with crystalline deposits that etched more slowly than the other dentin components, but etching rates could not be determined due to their irregular geometry. The intertubular dentin recession quickly reached a plateau after a depth change of <1 microm for all dentin types, in agreement with prior work. Mixed linear regression models indicated an important difference between the etching of sclerotic intertubular dentin and that of non-sclerotic root dentin that became apparent after 600 s (p = 0.037). The sclerotic intertubular dentin underwent less depth change at the plateau (558 nm) compared to normal root dentin (744 nm). In addition, normal root dentin underwent significantly greater recession than coronal dentin (p = 0.002). The results of this study indicate that intertubular sclerotic dentin from Cl V lesions etches differently than normal root dentin, and this may help explain the difficulties in restoring such lesions with current bonding procedures.

Acid Etching, Dental↗
PubMed1998

Temporal organization of sleep-wake states in preterm infants.

The development of temporal organization of sleep-wake states during the preterm period was examined. Seventy-one high-risk preterms from two cohorts were observed from 7 to 11 p.m. weekly from the time they were no longer critical until discharge. Mixed general linear model analyses found that with increasing postconceptional age, quiet waking, active waking, and sleep-wake transition bouts occurred more frequently, quiet sleep bouts occurred less frequently, and active waking and quiet sleep bouts increased in length. However, these developmental patterns were not stable over cohorts. On the other hand, the transitional probabilities between states were similar in both cohorts, providing evidence for biological bases for some aspects of temporal organization. Active sleep was pivotal in state transitions. Younger infants showed fewer transitions that did not involve active sleep. Thus, temporal organization is an early characteristic of sleep-wake states but is not a unitary phenomenon. Transitional probabilities remain relatively invariant, whereas bouts lengths and frequencies may be altered in different populations or by differing environmental conditions.

Age Factors↗
PubMed2000

Definition of individual bioequivalence: occasion-to-occasion versus mean switchability.

Two moment-based scaled definitions of individual bioequivalence are discussed. Based on a mixed effects linear model, their evaluations respectively lead to an unweighted (theta(11)) and a parametric (theta(15)) metric. The two metrics are estimated with respect to study design and two estimation methods. Results show that the two IBE metrics perform equivalently in the fully replicated design. In the semi-replicated design, the definition of theta(11) may not be valid while the evaluation of theta(15) results in a reduction of the weights in the mean difference and switchability components of the metric. Percentage rejection rates in the latter design indicate that theta(11) is more conservative than theta(15). This is because there is an increase of about 15 per cent in the producer risk in theta(11) relative to theta(15) compared to a 7 per cent increase in the consumer risk in theta(15) relative to theta(11). A further disadvantage of the design is that there is a 33 per cent loss in the subject-by-treatment variance efficiency which is reflected in a similar amount of decreased sensitivity to departures from perfect bioequivalence even when more subjects are used to equalize the number of exposure occasions in the two designs. It is concluded that a mean switchability criterion may be more appropriate from an interpretability perspective, the bootstrap resampling method used to evaluate individual bioequivalence based on theta(11) may need to be bias-corrected and that the semi-replicated design should be used cautiously.

Humans↗